fix: preserve web upload auto frame titles

[CircleCrop]

Motivation

• The scanner/fallback logic previously overwrote frame.title when showing fallback/full m2ts titles, losing the original automatic title; the UI must be able to switch presentation without mutating the upload plan.
• Provide a non-destructive way to show either the compact automatic title or a fuller m2ts-based title in the pairing preview and workbench.

Description

• Add a view-model title mode and separate title fields by introducing UploadPlanTitleDisplayMode and exposing autoTitle and fullTitle on FramePreviewRow, while leaving WebUploadFramePlan.title unchanged (files changed: web-upload-view-model.ts).
• Extend buildPlanView to accept a titleDisplayMode param and populate title, autoTitle, and fullTitle accordingly (option A implemented at view-model layer).
• Keep the workbench planRef immutable and store the current titleDisplayMode in React state; toggling rebuilds the PlanView from the original WebUploadPlan rather than mutating it (file changed: web-upload-workbench.tsx).
• Add a toggle button in PairingPreviewPanel with mode-aware copy that switches between 使用完整 m2ts-帧号 and 恢复自动帧号 and wired it to the workbench toggle handler (file changed: web-upload-pairing-preview.tsx).
• Add a regression test to web-upload-view-model.test.ts verifying switching to full titles and restoring back preserves the original automatic frame.title.

Testing

• Ran the focused unit tests with pnpm --filter @magic-compare/internal-site test -- web-upload-view-model.test.ts and fixed an initial parse mismatch; after the fix the test file passed.
• Ran the full internal-site test suite via pnpm --filter @magic-compare/internal-site test and all tests passed (120 passed).
• Ran lint (pnpm --filter @magic-compare/internal-site lint), typecheck (pnpm --filter @magic-compare/internal-site typecheck) and applied formatting with prettier; those checks completed without errors.

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Codex Task

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